Chitosan oligosaccharides, also known as oligosaccharides, have unique biological activities. For a long time, the molecular weight range of chitosan oligosaccharides is very vague. Glucosamine polymers with relative molecular weights ranging from hundreds to tens of thousands are called chitosan oligosaccharides, while chitosan oligosaccharides with relative molecular weights of hundreds differ greatly from chitosan oligosaccharides with relative molecular weights of tens of thousands from their physical and chemical properties to their biological activities. Chitosan oligosaccharides with high active fragments refer to glucosamine polymers with degree of polymerization of 2-10.

The general physical properties of Chitosan oligosaccharides are quite different from those of chitosan. Because of the decrease of molecular weight, the solubility of Chitosan oligosaccharide is greatly improved. Even if the pH value is above 10, Chitosan oligosaccharide can still be dissolved in water, while chitosan can only be dissolved in acidic solution. Enhancement of water solubility is a crucial factor affecting the physiological activity of chitosan oligosaccharides. Only when it is dissolved in water, it is possible for organisms to absorb and utilize chitosan oligosaccharides, showing physiological activity. However, chitosan oligosaccharides do not possess the properties of some polymer compounds of chitosan, such as film-forming properties, formation of high viscosity solutions, etc.

The solubility of chitosan oligosaccharide, especially its stability in solution, is of great significance for the application of chitosan oligosaccharides. Chitosan oligosaccharide molecule contains free amino group and hydroxyl group of hemiacetal. It is easy to condensate at high concentration and high temperature to form Schiff base. Chitosan oligosaccharide solution has strong reducibility, and oxidizes in the presence of oxidants or exposed to air. The color of Chitosan oligosaccharide solution will be darkened by these two reactions, so chitosan oligosaccharide solution should be sealed and stored at low temperature. Chitosan oligosaccharide can enhance its stability after salt formation.

Chitosan oligosaccharides are similar to chitosan in chemical properties. They contain hydroxyl and amino groups, and are easy to carry out chemical reactions (such as O-acylation and N-acylation, esterification, etherification, alkylation, oxidation, graft copolymerization and cross-linking). By introducing functional groups with different properties and functions into chitosan oligosaccharides, derivatives with unique functions can be obtained, thus further expanding the application fields of chitosan oligosaccharides.

Chitosan oligosaccharides have amino groups on C2 and hydroxyl groups on C3. Configuratively, they are flat bonds. This structure makes it chelate metal ions with a certain ion radius. Some metal ions with smaller radius (such as alkali metal and alkaline earth metal ions) do not chelate with chitosan oligosaccharides. The chelating strength of metal ions with larger ion radius to chitosan oligosaccharides increases with the increase of ion radius. Using this characteristic, chitosan oligosaccharides can be used as scavengers for some heavy metal ions (such as copper ion, lead ion, etc.) in the body, or as supplements for these ions by chelating chitosan oligosaccharides with some metal ions (such as zinc ion, etc.) in advance, which not only supplements these ions, but also has the health function of chitosan oligosaccharides.

Chitosan oligosaccharide is an alkaline substance, which can absorb hydrogen (H+) in solution. Many inorganic acids, organic acids and acidic compounds can be adsorbed by Chitosan oligosaccharide. When chitosan oligosaccharides are absorbed into the body, they can absorb acidic substances in the body, change the internal environment to a more alkaline direction, and improve the internal environment.